It is particularly preferred to employ Staphylococcal genes and gene products as targets for the development of antibiotics. The Staphylococci make up a medically important genera of microbes. They are known to produce two types of disease, invasive and toxigenic. Invasive infections are characterized generally by abscess formation effecting both skin surfaces and deep tissues. S. aureus is the second leading cause of bacteremia in cancer patients. Osteomyelitis, septic arthritis, septic thrombophlebitis and acute bacterial endocarditis are also relatively common. There are at least three clinical conditions resulting from the toxigenic properties of Staphylococci. The manifestation of these diseases result from the actions of exotoxins as opposed to tissue invasion and bacteremia. These conditions include: Staphylococcal food poisoning, scalded skin syndrome and toxic shock syndrome.
The frequency of Staphylococcus aureus infections has risen dramatically in the past 20 years. This has been attributed to the emergence of multiply antibiotic resistant strains and an increasing population of people with weakened immune systems. It is no longer uncommon to isolate Staphylococcus aureus strains which are resistant to some or all of the standard antibiotics. This has created a demand for both new anti-microbial agents and diagnostic tests for this organism.
SecA is an essential component of the bacterial protein secretion apparatus. This enzyme has been found in a wide variety of Gram-negative and Gram-positive bacteria. SecA proteins from different bacterial species are highly homologous and there is no known mammalian homologue making SecA an ideal target for therapeutic intervention. The proposed model of SecA activity (1,2) is based on the fact that SecA binds open-folded preproteins and interacts with a specific receptor complex at the cytoplasmic membrane. See Economou, A. and Wickner, W. (1994) Cell 78, 835-843; and Economou, A. et al. (1995) Cell 83, 1171-1181. ATP hydrolysis then provides the driving force for translocation of the preprotein by a unique mechanism involving transient insertion of SecA across the cytoplasmic membrane. This mechanism of bacterial translocation requires interaction of SecA with itself (SecA is functional as a dimer (Driessen, A. J. M. (1993) Biochemistry 32, 13190-13197)), ATP (van der Wolk, J. P. W. et al. (1995) Journal of Biological Chemistry 270, 18975-18982), preprotein, membrane phospholipids (Breukink, E. et al. (1995) Journal of Biological Chemistry 270, 7902-7907; Chen, X et al. (1996) Journal of Biological Chemistry 271, 29698-29706; van der Does, C. (1996) Molecular Microbiology 22, 619-629), SecB (Breukink, E. et al., supra) and the integral membrane components of the bacterial secretion apparatus (Snyders, S. et al. (1997) Journal of Biological Chemistry 272, 11302-11306). These numerous interactions provide us with many opportunities to inhibit the activity of this enzyme. Prom the above discussion we would expect inhibitors of SecA-mediated protein secretion to be broad spectrum and bactericidal without affecting eukaryotic protein secretion. For recent reviews of Sec dependent preprotein translocation see Wickner,W and Leonard,M. R. (1996) Journal of Biological Chemistry 271, 29514-29516; and den Blaauwen, T. and Driessen, J. M. (1996) Arch Microbiol 165, 1-8.
Clearly, there is a need for factors, such as the novel compounds of the invention, that have a present benefit of being useful to screen compounds for antibiotic activity. Such factors are also useful to determine their role in pathogenesis of infection, dysfunction and disease. There is also a need for identification and characterization of such factors and their antagonists and agonists which can play a role in preventing, ameliorating or correcting infections, dysfunctions or diseases.
The polypeptides of the invention have amino acid sequence homology to a known S.aureus NCTC 8325 secA protein.